The present invention relates in general to an electronic circuit for transmitting control signals to one or more receivers which in turn activate a load, such as a fluorescent lamp fixture. More particularly, the present invention relates to a transmitter adapted to control the energization of ballasted loads, such as fluorescent lights, and incorporates delayed synchronous channel multiplexing and frequency modulation to provide enhanced system efficiency.
A fluorescent lighting control system is described in U.S. Pat. No. 3,971,010. This system employs a frequency sensitive receiver circuit used to apply power to a fluorescent lighting fixture upon receipt of a proper activation signal. A radio frequency transmitter generates the control signals which are coupled through the lighting system power lines to the receivers. One of the problems associated with this system is that as more power receivers are added to the system, transmitter power requirements increase substantially. This increase in power requirements makes for a relatively complex and costly system particularly as the system requirements increase.
In other transmitter designs presently in use the efficiency of the product is relatively low. In one known design the efficiency is only at 25% (power out/power in) with most of the power being consumed in the output power transistors. Also, there is a need in existing systems for relatively complex field adjustments and adjustments in which the final settings are not necessarily independent. In one transmitter design there are actually a total of twelve field adjustments that are to be made. Furthermore, many of these adjustments require the use of special purpose tools.
Another problem associated with present transmitter designs is that they are adapted to have a continuous power output even after the receiver is turned on. This has the effect of increasing the cooling requirements and also is instrumental in increasing the cost of the overall device.
Also, with existing transmitters, cross channel interference exists providing undesired odd modulation and beat frequencies. Audible noise is generated as well as undesired off channel frequencies which further reduce field receiver yields and also reduce output transistor life.